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51.
The reaction of both cis- and trans-2,3-diphenyloxirane (7 and 4, respectively) with an excess of lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 2.5 mol%) in the presence of different carbonyl compounds as electrophiles (Barbier conditions) in THF at temperatures ranging between −80 and −50 °C gives the same organolithium intermediate 5 and consequently, the same 1,3-diols 6. In the case of cis-epoxide an inversion of the configuration at the benzylic carbanionic center can explain the obtained results. Only for the dicyclopropyl ketone derivative (6h) some amount (14%) of the corresponding epimer (6′h) resulting from a process with retention of the configuration of the intermediate is obtained. In representative cases, the structure of the final products (6) was unequivocally determined by X-ray diffraction analysis. 相似文献
52.
Tobias Wistuba Christian Limberg Peter Kircher 《Angewandte Chemie (International ed. in English)》1999,38(20):3037-3039
Not only capable of generating organic radicals by H abstraction, chromyl chloride can also trap them again (see scheme). This is confirmed by the crystal structure of a CrV oxo alkoxide, which was formed in three successive steps when bisadamantylidene oxide was allowed to react with CrO2Cl2. 相似文献
53.
二氧化碳是一种廉价、低毒、资源丰富的可用于有机合成的理想原料。由二氧化碳和环氧化合物共聚合成的脂肪族聚碳酸酯具有生物可降解性。自1969年井上祥平等发现二氧化碳和环氧化合物通过共聚反应合成脂肪族聚碳酸酯以来,利用二氧化碳制备高分子材料一直备受人们注目。该过程的关键是寻找具有高选择性的高效催化剂,三十余年来通过各国科学家的不懈努力已取得了不少成果,本文对其研究的最新进展进行了综述。 相似文献
54.
Florian Genrich 《Tetrahedron letters》2009,50(45):6187-6190
The reaction of a silyl-substituted thioacetal with ortho-difunctionalized benzenes as biselectrophiles allows access to multifunctional cyclooctanols. 相似文献
55.
56.
o-Carboxyhomomaleanilic acids (5) and o-carboxyhomophthalanilic acids (6) on treatment with sodium acetate-acetic anhydride furnished pyridobenzoxazinones (8) and isoquinolinobenzoxazinones (9) respectively in quantitative yields. Conversion of o-formylhomophthalanilic acid (7) to isocoumarinoquinoline (11) via 2-axo-3(o-carboxyphenyl)quinoline (10) is also described. 相似文献
57.
A simple method for the preparation of 9-alkyl- and 9-arylthio-phenanthrenes from 9-bromophenanthrene and a thiol is described. 相似文献
58.
A versatile heteropoly acid (H3PMo12O40)-catalyzed coupling of diarylmethanols with epoxides was established for the synthesis of polyaryl-substituted aldehydes. Furthermore, the catalytic system was also suitable for the reaction of diarylmethanols and diols/aldehydes. The application of such an earthabundant, readily accessible, and nontoxic catalyst provides a green approach for the construction of polyaryl-substituted aldehydes. 相似文献
59.
A highly regioselective method for the synthesis of β-iodohydrins and β-bromohydrins through direct ring opening of epoxides with elemental halogen in the presence of alumina-supported Schiff base complexes of Mn(II), Co(II), Ni(II) and Cu(II) as new catalysts is described. This method is regioselective under mild conditions in various aprotic solvents with high yields, even when sensitive functional groups are present. The catalysts are easily recovered and can be reused several times. 相似文献
60.
A zinc(II)porphyrin-based ion porous organic polymer (ZnTPyPBr4-iPOP) is successfully synthesized from newly designed pyridinium-functionalized cationic Zn-porphyrin monomer (ZnTPyPBr4) by free radical self-polymerization, and is employed as an efficient bifunctional heterogeneous catalyst for CO2 cycloaddition reaction with epoxides. The ZnTPyPBr4-iPOP exhibits excellent catalytic performance and good substrate expansion in CO2 cycloaddition reaction under solvent-free and cocatalyst-free conditions with a TOF as high as 15,500 h−1 for the cycloaddition of CO2 and epichlorohydrin. The synergistic effect of zinc(II)porphyrin as the Lewis acidic site and the Br− anion as the nucleophile in ZnTPyPBr4-iPOP responds to the high catalytic activity. Moreover, ZnTPyPBr4-iPOP can easily be recovered and reused at least seven times without the loss of activity. This work provides a valuable approach for the synthesis of novel and efficient heterogeneous catalyst for CO2 cycloaddition. 相似文献